The invention relates to a method for starting an internal combustion engine, and to a starting device for an internal combustion engine,
When an internal combustion engine is started, in conventional systems the internal combustion engine is rotated with the aid of a starter to a rotational speed of approximately 200 rev/min. On account of this low rotational speed, the suction-pipe pressure decreases only slowly, because the mass air flow sucked in by the internal combustion engine is very small. The fuel injected into the intake pipe can evaporate only inadequately at low intake-pipe temperatures (cold internal combustion engine) and at the high suction-pipe pressures, thus leading to poor mixture preparation. The result of this poor mixture preparation is that, during cold starting, large fuel quantities have to be injected in order to make it possible to start the internal combustion engine. The large fuel quantity, along with its poor propagation, is the main cause of the high pollutant emissions during cold starting. Since, in conventional systems, the starting emissions cannot even be treated subsequently because the exhaust gas catalytic converter has not yet reached its operating temperature, they make a decisive contribution to the overall emissions of a driving cycle. DE 198 52 085 C1 discloses a starting device for an internal combustion engine and a method for starting an internal combustion engine. To lower the exhaust-gas emissions, it is proposed to use two starters for starting the internal combustion engine, a first starter being activated at the commencement of the starting operation, which is deactivated after the internal combustion engine has reached a defined rotational speed, and a second starter being activated.
The second starter subsequently drives the internal combustion engine further to a defined desired rotational speed, after which, when the desired rotational speed is reached, fuel is injected for the first time for subsequent combustion. The first starter, also designated as a breakaway starter, in this case accelerates the internal combustion engine to about 200 rev/min. The second starter, also designated as a run-up starter, then accelerates the internal combustion engine to revolutions of about 700 rev/min to about 1000 rev/min. Moreover, it is proposed to use as a second starter an alternator of the internal combustion engine, in a reversal of the operation of said alternator as an electric drive for the internal combustion engine, and to drive the latter further to a defined desired rotational speed at which fuel is injected for the first time for subsequent combustion.
DE 197 05 610 A1 describes a starting or drive unit for an internal combustion engine of a motor vehicle, which carries out a different starting method when the engine is cold from that when the engine is warm. In this case, the drive unit is equipped with a conventional starter and with a starter/alternator machine. To start the cold engine, the starter is activated jointly with the starter/alternator machine, and, to start the warm engine, that is to say in the start/stop mode and in the full-swing mode, the starter/alternator machine alone is activated. Thus, depending the measured temperature of the internal combustion engine, either the conventional starter or the starter/alternator machine or both together are activated. In particular, at an internal combustion engine temperature of above 30xc2x0 C. to 40xc2x0 C., the starter function is performed solely by the starter/alternator machine. At higher temperatures above 40xc2x0 C., the starting function of the internal combustion engine is assumed solely by the wear-free starter/alternator. A cold-starting operation at temperatures below 30xc2x0 is carried by means of a conventional starter which for this purpose has a high reduction.
However, the use of two starters entails an appreciable outlay in terms of construction space and costs.
The object on which the invention is based is to specify a method for starting an internal combustion engine and a starting device, by means of which the emissions occurring during the starting of the internal combustion engine, in particular during a cold start, can be reduced in a simple way.
This object is achieved by means of the features of the inventive method and by means of the features of inventive device. Further advantageous developments are claimed.
To improve the poor mixture preparation within the range of the desired idling rotational speed, the internal combustion engine is rotated up to a high rotational speed ( greater than 800 rev/min) with the aid of a crankshaft starter alternator (KSG), without fuel injection and consequently starting of the internal combustion engine having taken place. In this case, the throttle valve is set to a defined value, preferably it is kept closed. Owing to the higher mass airflow of the internal combustion engine, the suction-pipe pressure falls rapidly. Fuel injection is enabled only when the suction-pipe pressure has undershot a predetermined threshold value.
What is achieved thereby is that, at a low suction-pipe pressure, the fuel quantity quickly evaporates, thus resulting in an improvement in mixture preparation and therefore both in a reduction of pollutant emissions and a fuel saving during starting.